Zouhair Tabka

Review on leptin and adiponectin responses and adaptations to acute and chronic exercise

Leptin and adiponectin represent two newly discovered adipose tissue derived hormones; that are both associated with health status and glucose and free fatty acid (FFA) metabolism. Moreover, acute and chronic exercises affect body composition, carbohydrate and lipid metabolism. It is thus interesting to evaluate the effects of physical exercise and training on leptin and adiponectin levels. It seems that leptin concentration is not modified after short-term exercise (<60 min) or exercise that generates an energy expenditure lower than 800 kcal. Leptin levels decrease after long-term exercise (≥60 min) stimulating FFA release, or after exercise that generates energy expenditure higher than 800 kcal. Adiponectin concentration presents a delayed increase (30 min) after short-term intense exercise (<60 min) performed by trained athletes. For adiponectin, limited data suggest that adiponectin concentration presents a delayed increase (30 min) after short-term intense exercise (<60 min) performed by trained athletes. It seems that adiponectin concentrations do not change in response to long-term exercise (≥60 min). Short-term training (<12 weeks) and long-term training (≥12 weeks) show contrasting results regarding leptin and adiponectin. Most training studies which improve fitness levels and affect body composition could decrease leptin and increase adiponectin concentrations.

Effects of a Back Squat Training Program on Leg Power, Jump, and Sprint Performances in Junior Soccer Players

Chelly, MS, Fathloun, M, Cherif, N, Amar, MB, Tabka, Z, and Van Praagh, E. Effects of a back squat training program on leg power, jump, and sprint performances in junior soccer players. J Strength Cond Res 23(8): 2241-2249, 2009-The aim of the present study was to investigate the effects of voluntary maximal leg strength training on peak power output (Wpeak), vertical jump performance, and field performances in junior soccer players. Twenty-two male soccer players participated in this investigation and were divided into 2 groups: A resistance training group (RTG; age 17 ± 0.3 years) and a control group (CG; age 17 ± 0.5 years). Before and after the training sessions (twice a week for 2 months), Wpeak was determined by means of a cycling force-velocity test. Squat jump (SJ), countermovement jump (CMJ), and 5-jump test (5-JT) performances were assessed. Kinematics analyses were made using a video camera during a 40-m sprint running test and the following running velocities were calculated: The first step after the start (Vfirst step), the first 5 m (Vfirst 5 meters), and between the 35 m and 40 m (Vmax). Back half squat exercises were performed to determine 1-repetition maximum (1-RM). Leg and thigh muscle volume and mean thigh cross-sectional area (CSA) were assessed by anthropometry. The resistance training group showed improvement in Wpeak (p < 0.05), jump performances (SJ, p < 0.05 and 5-JT, p < 0.001), 1-RM (p < 0.001) and all sprint running calculated velocities (p < 0.05 for both Vfirst step and Vfirst 5 meters, p < 0.01 for Vmax). Both typical force-velocity relationships and mechanical parabolic curves between power and velocity increased after the strength training program. Leg and thigh muscle volume and CSA of RTG remained unchanged after strength training. Back half squat exercises, including adapted heavy loads and only 2 training sessions per week, improved athletic performance in junior soccer players. These specific dynamic constant external resistance exercises are highly recommended as part of an annual training program for junior soccer players.

Effects of in-season short-term plyometric training program on leg power, jump- and sprint performance of soccer players.

Chelly, MS, Ghenem, MA, Abid, K, Hermassi, S, Tabka, Z, and Shephard, RJ. Effects of in-season short-term plyometric training program on leg power, jump- and sprint performance of soccer players. J Strength Cond Res 24(10): 2670-2676, 2010-Our hypothesis was that the addition of an 8-week lower limb plyometric training program (hurdle and depth jumping) to normal in-season conditioning would enhance measures of competitive potential (peak power output [PP], jump force, jump height, and lower limb muscle volume) in junior soccer players. The subjects (23 men, age 19 ± 0.7 years, body mass 70.5 ± 4.7 kg, height 1.75 ± 0.06 m, body fat 14.7 ± 2.6%) were randomly assigned to a control (normal training) group (Gc; n = 11) and an experimental group (Gex, n = 12) that also performed biweekly plyometric training. A force-velocity ergometer test determined PP. Characteristics of the squat jump (SJ) and the countermovement jump (CMJ) (jump height, maximal force and velocity before take-off, and average power) were determined by force platform. Video-camera kinematic analyses over a 40-m sprint yielded running velocities for the first step (VS), the first 5 m (V5m) and between 35 and 40 m (Vmax). Leg muscle volume was estimated using a standard anthropometric kit. Gex showed gains relative to controls in PP (p < 0.01); SJ (height p < 0.01; velocity p < 0.001), CMJ (height p < 0.001; velocity p < 0.001, average power p < 0.01) and all sprint velocities (p < 0.001 for V5m and Vmax, p < 0.01 for VS). There was also a significant increase (p < 0.05) in thigh muscle volume, but leg muscle volume and mean thigh cross-sectional area remain unchanged. We conclude that biweekly plyometric training of junior soccer players (including adapted hurdle and depth jumps) improved important components of athletic performance relative to standard in-season training. Accordingly, such exercises are highly recommended as part of an annual soccer training program.

Effect of Ramadan fasting on fuel oxidation during exercise in trained male rugby players

PURPOSE The aim of this study was to assess the effect of Ramadan fasting on substrate oxidation in trained athletes during moderate-intensity exercise. METHODS Nine trained men (age: 19+/-2 yr, Height: 1.78+/-0.74 m) were tested on three occasions: during a control period immediately before Ramadan (C), at the end of the first week (Beg-R), and during the fourth week of Ramadan (End-R). On each occasion, they performed submaximal cycle ergometer exercise, with work-rates that were increased progressively (loadings corresponding to 20, 30, 40, 50, 60% of Wmax). Steady-state substrate oxidation was evaluated by indirect calorimetry. RESULTS Participants showed significant decreases in body mass and body fat at the end of Ramadan, relative to initial control values (P<0.001). The daily food intake was also reduced during Ramadan (P<0.01). Haemoglobin concentrations and hematocrit were significantly higher at the end-Ramadan, both at rest (P<0.001 and P<0.0001 respectively) and after exercise, (P<0.05 and P<0.01 respectively) compared to control measurements made before Ramadan. At the end of Ramadan, our subjects had increased their fat utilization during exercise. The cross-over was observed at a higher intensity at the End-R (35% vs. 30% of Wmax, P<0.001). For the same power output, the Lipox max was also higher at the End-R, compared to control value (265+/-38 vs. 199.1+/-20 mg/min, P<0.001). CONCLUSION Ramadan fasting increases the lipid oxidation of trained athletes during submaximal exercise. The increased fat utilisation may be related to decreases in body mass and body fat content.

Effect of Time of Day and Partial Sleep Deprivation on Short‐Term, High‐Power Output

The purpose of this study was to determine whether delaying bedtime or advancing rising time by 4 h affects anaerobic performance of individuals the following day in the morning and afternoon. Eleven subjects participated in the study, during which we measured the maximal, peak, and mean powers (i.e., Pmax [force‐velocity test], Ppeak, and Pmean [Wingate test], respectively). Measurements were performed twice daily, at 07∶00 and 18∶00 h, following a reference normal sleep night (RN), a partial sleep deprivation timed at the beginning of the night (SDB), and a partial sleep deprivation timed at the end of the night (SDE), and oral temperature was measured every 4 h. Each of the three experimental conditions was separated by a one‐week period. Our results showed a circadian rhythm in oral temperature, and analysis of variance revealed a significant sleep×test‐time effect on peak power (Ppeak), mean power (Pmean), and maximal power (Pmax). These variables improved significantly from the morning to the afternoon for all three experimental conditions. Whereas the morning‐afternoon improvement in the measures was similar after the RN and SDB conditions, it was smaller following the SDE condition. There was no significant difference in the effect of the two sleep‐deprivation conditions on anaerobic performances at 07∶00 and at 18∶00 h under the SDB condition in comparison with the post‐reference night. However, the performance variables were significantly lower at 18∶00 h after the SDE condition. In conclusion, a 4 h partial sleep deprivation at the end of the night appears to be more disturbing than partial sleep deprivation at the beginning of the night.

Effect of individualized weight‐loss programmes on adiponectin, leptin and resistin levels in obese adolescent boys

Aim:  We investigate the effects of a 2‐month weight‐loss programme on plasma levels of adiponectin, leptin and resistin in obese adolescent boys.

Effect of Ramadan on the Diurnal Variation in Short‐Term High Power Output

This study examined the effects of Ramadan fasting on anaerobic performances and their diurnal fluctuations. In a balanced and randomized study design, 12 subjects were measured for maximal power (Pmax; force‐velocity test), peak power (Ppeak), and mean power (Pmean) with the Wingate test at 07:00, 17:00, and 21:00 h on four different occasions: one week before Ramadan (BR), the second week of Ramadan (SWR), the fourth week of Ramadan (ER), and two weeks after Ramadan (AR). There was an interval of 28 h between any two successive tests. Oral temperature was measured before each test. Under each condition, the results showed a time‐of‐day effect on oral temperature. Analysis of variance revealed a significant (Ramadan×time‐of‐day of test) interaction effect on Pmax. This variable improved significantly from morning to evening before Ramadan (1.1±0.2 W · kg−1), during the second week of Ramadan (0.6±0.2 W · kg−1), and two weeks after the end of Ramadan (0.9±0.2 W · kg−1). However, daily fluctuations disappeared during the fourth week of Ramadan. For Ppeak and Pmean, there was no significant Ramadan×test‐time interaction. These variables improved significantly from morning to evening before Ramadan ([1±0.3 W · kg−1] for Ppeak and [1.7±1.6 W · kg−1] for Pmean) and in the second week of Ramadan ([0.9±0.6 W · kg−1] for Ppeak and [1.7±1.5 W · kg−1] for Pmean). However, they were not affected by time‐of‐day in the fourth week of Ramadan. Considering the effect of Ramadan on anaerobic performances, in comparison with before Ramadan, no significant difference was observed during Ramadan at 07:00 h. The variables were significantly lower in the second week of Ramadan and in the fourth week of Ramadan at 17:00 h and 21:00 h. Pmean was not affected during the second week of Ramadan. In conclusion, the time‐of‐day effect on anaerobic power variables tends to disappear during Ramadan. In comparison with the period before Ramadan, anaerobic performances were unaffected in the morning but impaired in the evening during Ramadan.

Effects of two-month physical-endurance and diet-restriction programmes on lipid profiles and insulin resistance in obese adolescent boys

AIM The aim of this study was to assess the impact of a two-month programme of physical endurance and dietary restriction, alone and combined, on plasma lipids and insulin resistance in obese adolescents. METHODS A total of 24 obese adolescent boys participated in programmes of either dietary restriction (R), physical endurance at the point of maximum lipid oxidation (LIPOX(max)) (E) or diet combined with training (R+E). Anthropometric characteristics, metabolic measures and biochemical analyses were performed in all subjects before and after the interventions. An estimated insulin resistance was calculated using the homoeostasis model assessment (HOMA-IR) index. RESULTS At the end of the two-month programmes, adolescents in the R+E group showed greater reductions in body mass index (-3.9+/-0.7 kg/m(2)) and waist circumference (-12.3+/-4.8 cm) (P<0.001) than either the R or E group. A significant decrease (P<0.01) in HOMA-IR index (-2.13+/-0.11), plasma triglycerides, LDL and total cholesterol was also seen in the R+E group. Moreover, at the end of the programme, the ratio of HDL cholesterol to triglycerides was significantly increased from baseline in the R+E group (0.93+/-0.09 vs. 0.68+/-0.11; P<0.01). CONCLUSION Compared with either moderate physical endurance or dietary restriction, a combination of both resulted in a significant decrease in cardiovascular risk factors and HOMA-IR index in obese adolescent boys.

Effects of 8-week in-season upper and lower limb heavy resistance training on the peak power, throwing velocity, and sprint performance of elite male handball players.

Hermassi, S, Chelly, MS, Tabka, Z, Shephard, RJ, and Chamari, K. Effects of 8-week in-season upper and lower limb heavy resistance training on the peak power, throwing velocity, and sprint performance of elite male handball players. J Strength Cond Res 25(9): 2424-2433, 2011—The aims of this study were to test the potential of in-season heavy upper and lower limb strength training to enhance peak power output (Wpeak), vertical jump, and handball related field performance in elite male handball players who were apparently already well trained, and to assess any adverse effects on sprint velocity. Twenty-four competitors were divided randomly between a heavy resistance (HR) group (age 20 ± 0.7 years) and a control group (C; age 20 ± 0.1 years). Resistance training sessions were performed twice a week for 8 weeks. Performance was assessed before and after conditioning. Peak power (Wpeak) was determined by cycle ergometer; vertical squat jump (SJ) and countermovement jump (CMJ); video analyses assessed velocities during the first step (V1S), the first 5 m (V5m), and between 25 and 30 m (Vpeak) of a 30-m sprint. Upper limb bench press and pull-over exercises and lower limb back half squats were performed to 1-repetition maximum (1RM). Upper limb, leg, and thigh muscle volumes and mean thigh cross-sectional area (CSA) were assessed by anthropometry. Wpeak (W) for both limbs (p < 0.001), vertical jump height (p < 0.01 for both SJ and CMJ), 1RM (p < 0.001 for both upper and lower limbs) and sprint velocities (p < 0.01 for V1S and V5m; p < 0.001 for Vpeak) improved in the HR group. Upper body, leg, and thigh muscle volumes and thigh CSA also increased significantly after strength training. We conclude that in-season biweekly heavy back half-squat, pull-over, and bench-press exercises can be commended to elite male handball players as improving many measures of handball-related performance without adverse effects upon speed of movement.

Relationships of Peak Leg Power, 1 Maximal Repetition Half Back Squat, and Leg Muscle Volume to 5-m Sprint Performance of Junior Soccer Players

Chelly, MS, Chérif, N, Ben Amar, M, Hermassi, S, Fathloun, M, Bouhlel, E, Tabka, Z, and Shephard, RJ. Relationships of peak leg power, 1 maximal repetition half back squat, and leg muscle volume to 5-m sprint performance of junior soccer players. J Strength Cond Res 24(1): 266-271, 2010-Performance over very short distances (1-5 m) is important in soccer. We investigated this in 23 male regional-level soccer players aged 17.2 ± 0.7 years, filming body markers to determine the average velocity and acceleration over the first step (VS and AS) and the first 5 m (V5, A5). Data were related to scores on a force-velocity test, squat jump (SJ), countermovement jump (CMJ), and 1 maximal repetition (1 RM) half back squat. Leg and thigh muscle volumes were also assessed anthropometrically. V5 was positively correlated with leg and thigh muscle volumes (r = 0.61, p < 0.05; r = 0.43, p < 0.05, respectively), SJ power (absolute and relative to body mass, r = 0.45, p < 0.05; r = 0.43, p < 0.05, respectively), absolute force-velocity leg power (r = 0.49, p < 0.05), and 1 RM half back squat (r = 0.66, p < 0.001). The use of dimensional exponents did not change coefficients materially. VS was also correlated with leg muscle volume and 1 RM back half squat (r = 0.56, p < 0.01; r = 0.58, p < 0.01, respectively) and more weakly with force-velocity leg power and SJ force (r = 0.49, p < 0.05; r = 0.46, p < 0.5, respectively). However, the CMJ was unrelated to velocity or acceleration. Sprinting ability is correlated with measures of power and force such as the force-velocity test, SJ, and 1 RM half back squat; such measures thus offer useful guidance to soccer coaches who wish to improve the short-distance velocity of their players.